DBG system and method with adhesive layer severing

ABSTRACT

An array of grooves ( 23 ) is formed in a first side ( 12 ) of a wafer ( 10 ) during a wafer processing method. A back grinding tape ( 16 ) is adhered to the first side. An amount of material is removed from the second side ( 20 ) of the wafer. An adhesive layer ( 30 ) is applied to the second side. Dicing tape ( 24 ) is applied to the adhesive layer to create a first wafer assembly ( 32 ). The first wafer assembly is supported on a support surface ( 34 ) with the dicing tape facing the support surface and the back grinding tape exposed. The back grinding tape is removed and the adhesive layer is severed through the array of grooves to create individually removable die ( 28 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.10/959,713, filed Oct. 6, 2004, titled “DBG system and method withadhesive layer severing”, which claims the benefit of U.S. ProvisionalApplication No. 60/549,332, filed Mar. 2, 2004, titled “Substrateprocessing system and method”.

BACKGROUND

Wafer thinning technology is important to package development. Currentwafer thinning methods include the in-line wafer B/G (Back Grinding)system and the DBG (Dicing Before Grinding) process. The inline waferB/G systems have used the film adhesive process whereby the wafer isthinned by backgrinding and then is diced. However, a conventional DBGprocess did not use the film adhesive process because the separated diecreated by the DBG process had a tilt after B/G tape removing.

A conventional dice before grinding process is shown in FIGS. 1-7. FIG.1 illustrates a wafer 10 having a first or front side 12 being groovedusing a grinding wheel 14 or other grooving technique. FIG. 2illustrates adhering a back grinding tape 16 to side 12 using a roller18. The structure of FIG. 2 is then inverted exposing the second or backside 20 of wafer 10 at a material removal station 21 permitting agrinding wheel 22 to grind second side 20. Grinding wheel 22 removessufficient material to expose the grooves 23 formed by grinding wheel 14thus creating a diced wafer 25. FIG. 4 illustrates the application ofdicing tape 24 to second side 20 using a roller 26. The structure ofFIG. 4 is then inverted to permit back grinding tape 16 to be remove asillustrated in FIG. 5. FIG. 6 illustrates the structure of FIG. 5 withthe back grinding tape completely removed to expose the diced wafer 25.FIG. 7 is an enlarged view of a number of the diced die 28 of FIG. 6.FIG. 7 illustrates what is termed die tilt. Die tilt is created becausethe adhesive strength of dicing tape 26 is not sufficient to prevent theshifting of die 28 during the removal of back grinding tape 16. This dietilt is a problem because it makes picking and placing die 28 moredifficult thus increasing the complexity and cost of subsequentchipmaking operations.

SUMMARY

The present invention is directed to wafer processing method andapparatus in which an adhesive layer is used between a dicing tape and agrooved wafer. A second grinding or other severing step is used to severthe adhesive layer through the grooves. This use of the adhesive layerhelps to prevent undesirable die tilt; die tilt can create problemsduring the process of placing individual die onto a substrate.

A first aspect of the invention is directed to a wafer processingmethod. An array of grooves is formed in a first side of a wafer. A backgrinding tape is adhered to the first side. An amount of material isremoved from the second side of the wafer. An adhesive layer is appliedto the second side. Dicing tape is applied to the adhesive layer tocreate a first wafer assembly. The first wafer assembly is supported ona support surface with the dicing tape facing the support surface andthe back grinding tape exposed. The back grinding tape is removed andthe adhesive layer is severed through the array of grooves to createindividually removable die. The method may also include forming thearray of grooves in the first side of the wafer to a chosen depth withthe material removing step being carried out to create a wafer having achosen thickness. The forming and removing steps may be carried out sothat the chosen depth is greater than, for example about 20% greaterthan, the chosen thickness. The forming and removing steps may also becarried out so that the chosen depth is less than, for example about70-90% of, the chosen thickness so that the severing step severs boththe adhesive layer and wafer through the array of grooves.

A second aspect of the invention is directed to a wafer processingsystem for processing a wafer having an array of grooves formed in afirst side of a wafer and a back grinding tape adhering to the firstside. The assembly includes a material removal station at which anamount of material is removable from a second side of the wafer. Theassembly also includes a dicing tape application station at which thewafer has an adhesive layer and a dicing tape applied to the secondside, with the adhesive layer between the second side and the dicingtape, to create a first wafer assembly. A support surface stationcomprises a support surface. First wafer assembly transfer apparatus isarranged and adapted to transfer the first wafer assembly from thedicing tape application station to the support surface station with thedicing tape facing the support surface and the back grinding tapeexposed. The support surface station also includes means for removingthe back grinding tape and means for severing the adhesive layer throughthe array of grooves to create individually removable die.

Various features and advantages of the invention will appear from thefollowing description in which the preferred embodiments have been setforth in detail in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates grinding of the front side of a wafer using agrinding wheel;

FIG. 2 shows adhering a back grinding tape to the front side of a wafer;

FIG. 3 shows grinding of the backside of the wafer;

FIG. 4 illustrates mounting dicing tape on the ground backside of thewafer;

FIG. 5 illustrates the removal of the back grinding tape after thestructure of FIG. 4 has been flipped 180°;

FIG. 6 shows the structure of FIG. 5 after the removal of the backgrinding tape; and

FIG. 7 is enlarged illustration showing die tilt of the die of FIG. 6,FIGS. 1-7 being conventional.

FIGS. 8-14 illustrate a wafer processing system and method according tothe invention, FIG. 8 being similar to FIG. 4 with the addition of afilm adhesive layer between the dicing tape and the diced wafer;

FIG. 9 illustrates the structure of FIG. 8 flipped 180° with the backgrinding tape being removed;

FIGS. 10A and 10B are simplified cross sectional views taken along linesA-A and B-B of FIG. 9 illustrating that the grooves formed in the waferextended sufficiently far so that the grooves are exposed after thewafer grinding step of FIG. 3;

FIGS. 11A and 11B are views similar to FIGS. 10A and 10B of analternative embodiment in which the grooving step of FIG. 1 and thegrinding step of FIG. 3 are such that the grooves are not exposed afterthe grinding step, so that after the grinding step a portion of thewafer at the base of the grooves remains to further restrain subsequentdie tilt;

FIGS. 12 and 13 illustrate the second grinding or other severing stepremoving either (1) the film adhesive and a portion of the dicing tapeat the base of the grooves, according to the embodiment of FIG. 10B, or(2) the wafer remaining at the base of the grooves as well as the filmadhesive and a portion of the dicing tape at the base of the grooves,according to the embodiment of FIG. 11B; and

FIG. 14 is enlarged view similar to FIG. 7 but illustrating how theindividual die remain properly positioned after the removal of the backgrinding tape in FIG. 9 and the second grinding or other severing stepof FIGS. 12 and 13.

DETAILED DESCRIPTION

The invention will now be described in further detail by reference tothe drawings, which illustrate alternative embodiments of the invention.The drawings are diagrammatic, showing features of the invention andtheir relation to other features and structures, and are not made toscale. For improved clarity of presentation, in the FIGS. illustratingembodiments of the invention, elements corresponding to elements shownin other drawings are not all particularly renumbered, although they areall readily identifiable in all the FIGS.

FIGS. 8-14 illustrate a wafer processing system and method according tothe invention. The present invention may initially proceed as describedabove with reference to FIGS. 1-3 with like reference numerals referringto like elements but with the following distinctions. The groove formingstep of FIG. 1 is carried out so that grooves are formed in first side12 to a chosen depth and the material removing step of FIG. 3 is carriedout at material removal station 21 to create a diced wafer 25 having achosen thickness. The groove forming and material removing steps may becarried out so that the chosen depth of grooves 23 is greater than, suchas 20% greater than, the chosen thickness, as in the prior art and asillustrated in FIGS. 10A and 10B. However, the groove forming andmaterial removing steps may also be carried out so that the chosen depthof grooves 23 is less than the chosen thickness, such as 70-90% of thechosen thickness, as is illustrated in FIGS. 10A and 10B.

FIG. 8 is similar to FIG. 4. However, adhesive layer 30, preferably afilm adhesive layer, is positioned at a dicing tape application station31 between dicing tape 24 and diced wafer 25 to create a first waferassembly 32. Dicing tape 24 and adhesive layer 30 may be simultaneouslyapplied to diced wafer 25 as a multiple-layered tape or they may beapplied separately. Adhesive layer 30 maybe a conventional filmadhesive, such as available from Lintec Corporation as Lintec LE5000.The thickness of the film adhesive used to create adhesive layerspreferably ranges from 20-75 μ, and preferably about 40 μ.

FIG. 9 illustrates the first wafer assembly 32 of FIG. 8 flipped 180°and resting on a vacuum table 34, or other support surface, at a supportsurface station 36. Back grinding tape 16 is shown being removed atsupport surface station 36.

FIGS. 10A and 10B are simplified cross sectional views taken along linesA-A and B-B illustrating that grooves 23 formed in wafer 10 extendedsufficiently far so that after the wafer grinding step, such as in FIG.3, grooves 23 are exposed. That is, the groove forming step of FIG. 1 iscarried out so that grooves 23 are formed in first side 12 to a chosendepth and the material removing step of FIG. 3 is carried out to createa diced wafer 25 having a chosen thickness. The groove forming andmaterial removing steps are be carried out so that the chosen depth ofgrooves 23 is greater than, such as 20% greater than, the chosenthickness to create the structure illustrated in FIGS. 10A and 10B.

FIGS. 11A and 11B illustrate an alternative embodiment in which thegrooving step of FIG. 1 and the grinding step of FIG. 3 are such thatgrooves 23 are not exposed after the grinding step. Therefore, a portion37 of diced wafer 25 at the base of grooves 23 remains to furtherrestrain subsequent die tilt. That is, the groove forming and materialremoving steps are carried out so that the chosen depth of grooves 23 isless than the chosen thickness, such as 70-90% of the chosen thickness.

The use of adhesive layer 30, as with FIG. 10B, or both adhesive layer30 and wafer portion 37, as with FIG. 11B, helps to ensure that dietilt, illustrated in FIG. 7, does not occur. However, this additionalstability requires an additional severing step to make die 28individually removable. FIGS. 12 and 13 illustrate a second grinding orother severing step 38 removing either (1) adhesive layer 30 and aportion of dicing tape 24 at the base of grooves 23 according to theembodiment of FIG. 10B, or (2) a wafer portion 37, adhesive layer 30 anda portion of dicing tape 24 at the base of grooves 23 according to theembodiment of FIG. 11B. FIG. 14 is enlarged view similar to of FIG. 7but illustrating how the individual die 28 remain properly positionedafter the removal of back grinding tape 16 in FIG. 9 and second grindingor other severing step 38 of FIGS. 12 and 13.

Conventional or unconventional wafer transfer apparatus may be used toperform the various functions and tasks discussed above, such as totransfer first wafer assembly 32 from dicing tape application station 31to support surface station 36. An example of an appropriate wafertransfer apparatus is that sold by Tokyo Seimitsu Co Ltd. (TSK) ofTokyo, Japan. Back grinding tape 16 may be removed using, for example,equipment also sold by TSK. The severing step of FIG. 12 may be carriedout using, for example, dicing saw equipment sold by Disco Corporationof Tokyo, Japan.

Modification and variation can be made to the disclosed embodimentswithout departing from the subject of the invention as defined infollowing claims.

Any and all patents, patent applications and printed publicationsreferred to above are incorporated by reference.

Other embodiments are within the scope of the invention.

1. A semiconductor wafer processing system, comprising: a first waferprocessing station for (a) forming an array of grooves in a first sideof a semiconductor wafer to a chosen depth which is 70-90 percent of achosen thickness of the semiconductor wafer, (b) applying aback-grinding tape to the first side of the semiconductor wafer, (c)back-grinding a second side of the semiconductor wafer until thesemiconductor wafer has the chosen thickness, wherein the back-grindingremoves a portion of the second side of the semiconductor wafer withoutexposing the grooves from the second side of the semiconductor waferwhich leaves a remaining portion across the second side of thesemiconductor wafer, (d) applying an adhesive layer to the remainingportion of the second side of the semiconductor wafer, and (e) applyinga first side of dicing tape over the adhesive layer; and a second waferprocessing station having a vacuum table for securing a second side ofthe dicing tape, the second wafer processing station including, (f)means for removing tho back-grinding tape, and (g) means for severingthe remaining portion of the second side of the semiconductor wafer,adhesive layer, and dicing tape to provide individually removable diefrom the semiconductor wafer without having incurred die tilt from thefirst and second wafer processing station features (a) - (g).
 2. Thesemiconductor wafer processing system of claim 1, wherein the adhesivelayer has a thickness of 20-75 micrometers.
 3. The semiconductor waferprocessing system of claim 1, wherein the adhesive layer includes a filmadhesive.
 4. The semiconductor wafer processing system of claim 1,wherein the means for severing includes a grinding wheel.
 5. Thesemiconductor wafer processing system of claim 1, wherein the adhesivelayer and dicing tape are applied simultaneously.
 6. A semiconductorwafer processing system, comprising: a first wafer processing stationfor (a) forming an array of grooves in a first side of a semiconductorwafer to a chosen depth which is about 20 percent greater than a chosenthickness of the semiconductor wafer, (b) applying a back-grinding tapeto the first side of the semiconductor wafer, (c) back-grinding a secondside of the semiconductor wafer until the semiconductor wafer has thechosen thickness, wherein the back-grinding exposes the grooves from thesecond side of the semiconductor wafer, (d) applying an adhesive layerto the second side of the semiconductor wafer, and (e) applying a firstside of dicing tape over the adhesive layer; and a second waferprocessing station having a vacuum table for securing a second side ofthe dicing tape, the second wafer processing station including, (f)means for removing the back-grinding tape, and (g) means for severingthe adhesive layer and dicing tape to provide individually removable diefrom the semiconductor wafer without having incurred die tilt from thefirst and, second wafer processing station features (a) - (g).
 7. Thesemiconductor wafer processing system of claim 6, wherein the adhesivelayer has a thickness of 20-75 micrometers.
 8. The semiconductor waferprocessing system of claim 6, wherein the adhesive layer includes a filmadhesive.
 9. The semiconductor wafer processing system of claim 6,wherein the means for severing includes a grinding wheel.
 10. Thesemiconductor wafer processing system of claim 6, wherein the adhesivelayer and dicing tape are applied simultaneously.
 11. A semiconductorwafer processing system, comprising: a first wafer processing stationfor (a) forming an array of grooves in a first side of a semiconductorwafer to a chosen depth, (b) applying a back-grinding tape to the firstside of the semiconductor wafer, (c) back-grinding a second side of thesemiconductor water until the semiconductor wafer has a chosenthickness, (d) applying an adhesive layer to the second side of thesemiconductor wafer, and (e) applying a first side of dicing tape overthe adhesive layer; and a second wafer processing station having asupport table for securing a second side of the dicing tape, the secondwafer processing station including, (f) means for removing theback-grinding tape, and (g) means for severing the adhesive layer anddicing tape to provide individually removable die from the semiconductorwafer without having incurred die tilt from the first and second waferprocessing station features (a) - (g).
 12. The semiconductor waferprocessing system of claim 11, wherein the chosen depth of the groovesis 70-90 percent of the chosen thickness of the semiconductor wafer. 13.The semiconductor wafer processing system of claim 11, wherein thechosen depth of the grooves is 20 percent greater than the chosenthickness of the semiconductor wafer.
 14. The semiconductor waferprocessing system of claim 11, wherein the adhesive layer has athickness of 20-75 micrometers.
 15. The semiconductor wafer processingsystem of claim 11, wherein the adhesive layer includes a film adhesive.16. The semiconductor wafer processing system of claim 11, wherein thefirst wafer processing station includes a grinding wheel.
 17. Thesemiconductor water processing system of claim 11, wherein the means forsevering includes a grinding wheel.
 18. The semiconductor waferprocessing system of claim 11, wherein the means for severing occursthrough the grooves.
 19. The semiconductor wafer processing system ofclaim 11, wherein the adhesive layer and dicing tape are appliedsimultaneously.